Multi-level approach for the assessment of bridge and viaducts within road networks

The recent tragic events that involved bridges and viaducts, happened in the Italian road network in the last 15 years, have highlighted the high level of risk and fragility of the national infrastructural heritage, characterized by a very high number of structures, different each other structurally and geometrically, most of them built in the second postwar period with low quality materials and not enough maintained over the years. Therefore, the need to perform a structural risk assessment of bridges and viaducts is a current and urgent issue. Applying the currently existing methods, codified by Eurocodes or national standards, for the structural assessment of all bridges in the Italian territory would require temporal and economic resources not easily sustainable by the Public Administrations, especially considering that most part of the Italian road network is managed by little realities, such as Provinces and Municipalities. These considerations highlighted the need to define and develop simple and expeditious methods to evaluate the structural risk associated to all bridges in order to define an intervention priority, classifying the structures and identifying those that need more in-depth investigations and more sophisticated analysis. The goal is passing from simple and quick evaluations on a territorial macro-scale to a more punctual evaluations to apply on a case by case basis. In this paper, a method of classification of the bridges and viaducts, based on the “warning level” associated to each one, is proposed. The “warning level” is defined according the usual framework of the risk definition and taking into account all the factors that influence the structural risk, such as the structural defectiveness level, the static scheme’s vulnerability, the rapidity of the evolution of deterioration and the type and amount of traffic flows. The definition of the “warning level” is based on the results of visual inspections of the structures, that allow to evaluate the state of conservation of the bridges and to know their main characteristics. Combining the state of conservation with the other factors, like the construction period, it is possible to make a reliable estimate of the structural risk associated with each bridge and to evaluate the necessity and the urgency of an intervention. The proposed methodology was calibrated on the basis of the study of the existing scientific literature in this field and the results of over 100 visual inspections of bridges in Province of Pisa and in Province of Caserta. This paper presents the main characteristics of the methodology and its application to a sample of bridges.